The field of electrosurgery includes a number of loosely related surgical techniques which have in common the application of electrical energy to modify the structure or integrity of patient tissue. Electrosurgical procedures usually operate through the application of very high frequency currents to cut or ablate tissue structures, where the operation can be monopolar or bipolar. Monopolar techniques rely on external grounding of the patient, where the surgical device defines only a single electrode pole. Bipolar devices comprise both electrodes for the application of current between their surfaces.
Electrosurgical procedures and techniques are particularly advantageous since they generally reduce patient bleeding and trauma associated with cutting operations. Additionally, electrosurgical ablation procedures, where tissue surfaces and volume may be reshaped, cannot be duplicated through other treatment modalities.
Present electrosurgical techniques used for tissue ablation suffer from an inability to control the depth of necrosis in the tissue being treated. Most electrosurgical devices rely on creation of an electric arc between the treating electrode and the tissue being cut or ablated to cause the desired localized heating. Such arcs, however, often create very high temperatures causing a depth of necrosis greater than 500 μm, frequently greater than 800 μm, and sometimes as great as 1700 μm. The inability to control such depth of necrosis is a significant disadvantage in using electrosurgical techniques for tissue ablation, particularly in arthroscopic procedures for ablating and/or reshaping fibrocartilage, articular cartilage, meniscal tissue, and the like.
Generally, radiofrequency (RF) energy is extensively used during arthroscopic procedures because it provides efficient tissue resection and coagulation and relatively easy access to the target tissues through a portal or cannula. However, a typical phenomenon associated with the use of RF during these procedures is that the currents used to induce the surgical effect can result in heating of electrically conductive fluid used during the procedure to provide for the ablation and/or to irrigate the treatment site. If the temperature of this fluid were allowed to increase above a threshold temperature value, the heated fluid could result in undesired necrosis or damage to surrounding neuromuscular and/or soft tissue structures.
Previous attempts to mitigate these damaging effects have included either limiting the power output of the RF generator or to include a suction lumen on the distal tip of the electrosurgical device to continuously remove the affected fluid from the surgical site and thereby reduce the overall temperature. These solutions may be effective but are limited and they do not allow for direct feedback based upon the actual temperature of the fluid within the joint space.
There have been numerous RF based systems introduced into the market that make use of a temperature sensor in order to monitor the temperature of tissue at or near the electrode. However, these systems do not include any mechanisms to monitor the temperature of the fluid within a body space, such as a joint space.